Autoregulation of the Modified Low Density Lipoprotein Receptor in Human Monocyte-derived Macrophages

Regulation of the macrophage receptor for modified low density lipoprotein (LDL) was evaluated using human monocyte-derived macrophages and acetyl LDL. Factors that regulate native LDL receptor activity in other cell types, such as the cholesterol content of the incubation medium, insulin, and platelet-derived growth factor had no effect on acetyl LDL degradation. Conditioned medium from mature macrophages significantly stimulated acetyl LDL degradation and enhanced cholesterol esterification by freshly isolated monocytes. Time course studies indicated that increasing time in culture was associated with increasing potency of the stimulating activity of macrophage-conditioned medium. These data suggest that a macrophage secretory product may be a prime modulator of modified LDL receptor activity on monocyte-macrophages, thus exerting an autocrine regulatory effect. The positive autoregulation of the human macrophage receptor for modified LDL could accelerate cellular cholesteryl ester accumulation and macrophage-derived foam cell formation.